The present invention relates to a thermal printer and to a thermal printing method, including flattening the surface of a recording paper on which an image has been printed.
One example of a known thermal printing method is a sublimation type thermal printing method, wherein an ink film is interposed between a thermal head and a recording paper, the ink film is heated from the back surface thereof, and heat activated dye is transferred to an image receiving layer of the recording paper and fixed therein. This sublimation type thermal printing method is suitable for printing a half-tone image such as a photographic picture because the method can record dots whose density is proportional to the thermal energy. The ink film has a thin film on which cyan, magenta, and yellow sections are formed alternately. There is also a known ink film having black sections in addition to the three color sections.
It is known that if an image is printed with a sublimation type thermal printer, irregular undulation is formed on the surface of a recording paper by the thermal head in accordance with image density and with heat and pressure thereby resulting in a finished image that is partially unclear and not glossy. To solve this problem, as disclosed in Japanese Laid-open Publication No. 62-132680, there has been proposed a method of flattening the surface of a recording paper wherein a heating roller or belt with a flat surface is pushed against the recording paper after printing to subject the recording paper to thermal processing.
However, this conventional flattening process requires that a roller or belt be mounted in addition to a heater on a thermal printer, resulting in a large overall dimension. Further, since the distribution of undulation on the recording paper surface is irregular, sufficient flattening is difficult in a direction perpendicular to the direction of feeding the recording paper, even if the heating roller or belt is pressed in contact with the whole area of the recording paper.